Description: (Taken directly from the application) Mutations in the PKD 1 gene cause 80-90% of the cases of polycystic kidney disease. These mutations give rise to cyst growth and enlargement, ultimately leading to the development of polycystic kidneys and to extrarenal manifestations of the disease, including Ever and pancreatic cysts, cerebral and aortic aneurysms, and heart valve defects. However, the function of the normal PKD 1 gene is not known and thus it is not understood how mutations in the PKD1 gene give rise to the disease pathogenesis associated with PKD. As such, it will be important to understand the biochemical and cellular functions of the PKD1 gene in order to gain insight into the aberrant mechanisms that occur upon initiation of the disease, and to design therapeutic interventions to treat or slow disease progression. The PKD 1 gene encodes an approximately 400 kDa protein, polycystin-1, that has been hypothesized function as a plasm membrane receptor. Sequence analysis has revealed that the C-terminal cytosolic domain of polycystin-1 has a number of conserved motifs that suggest that it functions by mediating signal transduction. This idea is supported by our new preliminary evidence that demonstrates that the C-terminal tail of polycystin-1 binds and activates heterotrimeric G-proteins; in vitro, and that it can be phosphorylated both in vitro and in vivo. If it can be confirmed that polycystin-1 directly interacts with heterotrimeric G-proteins, polycystin will be placed in the mainstream of a number of possible signal transduction pathways. Our general hypothesis is that polycystin-1 functions as a G-protein coupled receptor. This hypothesis will be tested by the following Specific Aims: Aim 1. Amino acid residues required for the in vitro binding interaction between polycystin-1 and heterotrimeric G-proteins will be determined. Aim 2. The potential for polycystin-1 to engage in heterotrimeric G-protein coupled signal transduction will be determined. Aim 3. The potential for polycystin-1 to interact with regulators of heterotrimeric G-protein coupled receptors will be determined. Aim 4. The importance of the conserved G-protein activation domain will be tested in transgenic mice.